Polycystic Kidney Diseases (PKD) are the leading cause of end-stage renal failure and require extensive treatments, such as dialysis and kidney transplantation. Only limited forms of therapy for PKD exist, since the molecular mechanism underlying the formation of renal cysts is still poorly understood. Over the years considerable progress has been made in identifying genes mutated in human forms of PKD and in the development of animal models to study the pathogenesis of these detrimental diseases. Besides the analysis of mouse and rat PKD models, the study of the more primitive pronephric kidney has emerged as an alternative to studying PKD. The simplicity and the rapid development of the pronephros is a very attractive model to study the molecular mechanism underlying the epithelial malformations causing PKD. Loss-of-function studies using morpholino antisense oligomers provide a fast and easy way to analyze gene function within weeks instead of the rather slow genetic manipulations in mouse. This facilitates a more exploratory approach towards kidney development and its perturbation during PKD. This proposal studies Bicaudal-C, a gene mutated in the bpk and jcpk mouse models of PKD. In a previous study, the function of the Xenopus homologue of Bicaudal-C during germ layer patterning was analyzed. Here, we propose to study the role of Bicaudal-C during pronephros development in the amphibian, Xenopus laevis, by eliminating the protein in the pronephros using antisense morpholino oligomers. We will test the hypothesis that loss-of-Bicaudal-C in the pronephros induces epithelial abnormalities similar to those described in human and mouse PKD. Molecular markers will be used to characterize the onset and the progression of the phenotype. The study will also test whether elimination of Bicaudal-C leads to defects in the function of the primary cilia present on renal epithelial cells. The results will provide novel insights into PKD and will be directly applicable to mammalian studies of PKD. Furthermore, this study will provide the basis for future studies of PKD in Xenopus, using the fast developing amphibian model system to characterize the underlying biological and biochemical pathways leading to PKD.